Repeater apparatus for carrier systems



FQh. 6, 19232" L.- -ESPENSCH ED. REPEATER APPARATUS FOR CARRIER SYSTEM-S.

FILED JUNE 199 1919.

2 SHEETS'SHEET I INVEIYTOR. 6. Ape/25612; 6d BY ATTORNEY 4. 8 T 0W & 3 w 44 s 4, a l m Feb, 6, ,1 923.

L. ESPENSCHIED. REPEATER APPARAT us FOR CARRIER YSTEMS ILED JUNE 19. 1919.

IN VEN TOR.

% yaewzed B Y MO RNE Y Patented Feb. (5, 1923.

Uhii'lii. STTES FATE. OFICE.

LLOYD SPENSCHIEI), 0 HOLLIS, NEW? YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

REPEATER APPARATUS FOR CARRIER SYSTEMS.

Application filed June 19, 1919. Serial No. 305,389.

To all 1.0 Ito m it may concern Be it known that I, LLOYD ESPENSCHIED, residing at Hollis, Long Island, in the county of Queens and State of New York, have invented certain Improvements in Repeater r-Xpparatus for Carrier Systems, of which the following is a specification.

This invention relates to repeater circuits and more particularly to repeater circuits adapted for the amplification of high frequency carrier currents.

Where a carrier system is superposed on an ordinary low frequency transmission line such as a telephone or telegraph line and such a line includes a repeater for amplifying the low frequency signals transmitted thereover, it is necessary to make some spe cial provision for amplifying the carrier frequencies transmitted over the line since the low frequency repeater is not so designed as to efliciently amplify the higher frequencies used for carrier transmission. Since it is desirable to superpose the carrier system upon the low frequency system with the least possible change and reorganization of the latter, it is desirable that some arrangement be provided whereby the high frequency oscillations may be amplified without disturbing the low frequency repeater organization.

An important feature of the present invention is the provision of means for amplifying the hi h frequency carrier oscillations without disturbing the low frequency repeater. This feature as well as other aims of the invention, are realized in a specially designed rweater adapted to amplify all of the carrier frequencies transmitted over the low frequency signalling circuit, and in an arrangement of said special repeater to operate in parallel with the low frequency repeater no mally associated with the lines. The invention also provides for substanl l; lly PW-W'tliidlig the carrier oscillations from be 1 'aii:-:n:iitted to the low frequency rcpea .er, and for prerentiug the transmissions of the low frequency sigi'ialling currents to the special high frequency repeater. In this manner the low frequency channel. and the high frequency channels are maintained distinct from each other and the high frequency apparatus in the repeater stations may be imposed upon the ordinary low frequency system or removed therefrom without materially affecting the organization or properties thereof.

The invention may now be more fully understood by reference to the following description When read in connection with the accompanying drawing, Figure 1 of which discloses a circuit arrangement of one embodiment of the invention and Fig. 2 of which illustrates a modification.

In Fig. 1 ML and ML designate sections of an ordinary low frequency transmission circuit such as a telephone circuit, these sections being interconnected by a two-way repeater of well known construction, comprising amplifiers AE and AW for amplifying currents transmitted in opposite directions. The transmission line sections ML and ML, are balanced with respect to the repeater by means of artificial lines MN and MN respectively. The output circuits 1 and 2 of the amplifiers AE and ATV are associated with the transmission line sections and cor: responding artificial lines through the usual three-winding transformers T and T'. The input circuits 3 and 4 are associated with the input bridges 5 and 6 through transformers 7 and 8.

The repeater apparatus so far described is of the ordinary construction employed in telephone practice and its operation is well understood. In order to amplify the carrier frequencies, however, a specially designed repeater is necessary. For this purpose the amplifying arrangement shown in the lower part of the diagram is connected to the line sections ML and ML, through carrier transmission branches CB and 0B,. This special repeater includes two one-way amplifying arrangements A l? and A,l/V. Each of these amplifying arrangements con sists of a duplex two-stage amplifier of the so called push-pull type. The amplifying arrangement A R comprises a pair of aniplifying vacuum tubes 9 and 10 in tandem with each other and in parallel with another pair of tandem tubes 11 and 12. Similarly the amplifying arrangement A,W includes a pair of tandem vacuum tube amplifiers 13 and 14 connected in parallel. with. a similar ciated through transformers 19 and 20 with intermediate circuits 21 and 22 which are connected through three-winding transformers 23 and 24 with the carrier branches (TB and CB, respectively. The input circuits 25 and 26 are associated through transformers 27 and 28 with the input bridges 29 and 30.

Since the carrier frequencies after being transmitted over lines of considerable length will be more or less attenuated, depending upon the frequency, it .is desirable that the amplitudes of the several carrier frequencies should be equalized. For this purpose equalizing arrangemen s 31 and 32 may be provided in the input bridges 29 and 30, respectively. The general principles pertaining to equalizers of this character are full Y set forth in the U. S. application of Bay Hoyt, Serial No. 242,567, filed June 29, 1918, and as these equalizing arrangements constitute no part of the present invention they need not be described in detail herein. In order to prevent carrier frequencies from being transmitted to the low frequency repeater, low frequency filters LF and LF are provided. \Vhile these filters may be of any desired character they are preferably broad band filters of the general type disclosed in U. S. patents to George A. Campbell, 1,227,113 and 1,227,114 dated May 22, 1917. These filters comprise a plurality of sections, each consisting of series inductance and shuntcapacity, so designed as to freely transmit frequencies which lie within the limits of ordinary signal transmission, while substantially extinguishing frequencies lying above said limit. In the special case herein illustrated in which the arrangement is applied to telephone transmission the filters LF and LF should transmit with negligible within the range of ordinary telephone transmission While practically extinguishing higher frequencies. In order to balance these filters with respect to the low fre quency repeater, balancing net works LF and LF, are provided. These balancing net works may be filters duplicating the filters LF and LF, or they may simply be net works so designed as to have electrical characteristics simulating those of the filters.

In order to prevent the transmission of low frequency currents to the hi h frequency repeater. high frequency filters F and HF, are included in the carrier branches CB and B,. These filters are also of the general type disclosed in the Campbell patents above referred to and each consists of a plurality of sections comprisin series capacity and shunt inductance. 'he elements of these filters are so proportioned as to freely transmit a band of frequencies above the upper limiting frequency of ordinary si a1 transmission while substantially extinguishing attenuation frequencies lying currents below said limit. In the particular case illustrated, which applies to telephone transmission, the filters HF and H F would be designed to freely transmit froquencies lying above the upper limits of ordinary telephonic transmission, while extinguishing frequencies lying below said limit. In order to balance the filters HF and HF,, balancing net works HF and HF, are provided. These balancing net works ma simply be filters duplicating the filters H and HF or they may consist of net works so designed as to have electrical characteristics simulating those of the filters HF and HF,. Balancing net Works M N and M N are also provided, these balancing net works being so designed as to simulate the characteristics of the apparatus connected across the terminals of the filters HF and HF,.

The operation of the circuit may now be readily understood and is as follows: Low frequency currents flowing over the line ML are transmitted over the filter LF and from the input bridge 5, through the transformer '7, an input circuit 3, to the amplifier AE. Upon being amplified the currents are trans mitted from the output circuit 1, through the transformer T where the energy divides, part flowing through the filter LF to the line section ML and part flowing through the balancing arrangement LF, to the net Work MN,. Low frequency transmission in the opposite direction will take place in a similar manner and need not be described.

High frequency carrier oscillations incoming from the line section ML will be transmitted through the high frequency filter HF and over the carrier branch CB to the input bridge 29. After being equalized by the equalizer 31, the carrier frequencies are transmitted through the transformer 27 to the duplex amplifying arrangement A 1 1. The construction of this duplex amplifying arrangement is such that the two sides of the circuit are balanced so that suhstantially no current variations take place in the common paths of the input and output circuits of the tubes connected in parallel and the resultant effect is that of current "ariation flowing serially over the amplificr conductors indicated by heav lines. This balanced construction of the amplifying arrangement results in less distortion of the oscillations. The :unplifieijl oscillations appearing in the output circuit 17 are transmitted through the transformer 19 and over the intermediate circuit 21, to the threw winding transformer 23, where the energy divides, part flowing over the carrier branch (1B, and through the high frequency filter I-lF to the main line section ML and part flowing through the balancin arrangement HF, to the artificial line M i h. Transmission in the opposite direction takes place in a he further dethe proper repeaters are arranged upon the repeater side of the balancing transformer instead of upon the line side. The same reference, characters are used to designate elements of this figure which also occur in Fig. 1.

Referring to Fig. 2 themain lines'l ili and ML are balanced by networks or artificial lines MN and Mil respectively, and trans formers 4:0 and 41 are provided for associating input circuits l-L and output circuits OO withv the main line sections. The input circuit I is provided with a high frequency branch HI and a low frequency branch Ll, the former branch including the high frequency filter HFE and the branch LI including the low frequency filter LEE. These filters are similarto filters Hi and LF respectively, of Fig. 1, the filter HFE passing a band of frequencies sufficiently broad to include the carrier frequencies of the several carrier channels while excluding frequencies below the upper limit used. in ordinary telephone transmission, and the filter LEE passing ordinary telephonic frequencies but substantially excluding higher frequencies. The high frequency branch Hi is connected to a repeaterunit A E for amplifying carrier frequencies transmitted from west to east, said repeater having its output circuit associated with a high frequency branch H0 of the. output connection 0 through the high frequency filter HFE similar to filter HFE. In a similar manner the low frequency branch Ll is con nected through the filter LFE to an amplifying tube AR for amplifying telephone currents transmitted from west to east. The amplifier ALE is connected through asimilar filter Ll ll to a low frequency branch llrO of theoutput col'uieetion 0, leading to the line ML. i

The input connection l, iron the line ML is. similarly provided rvith high frequency and low frequency branches ill, and Li the former beingconnected through a high frequency filter ill-Fil similar to H FE to an amplifier unit AMT for an|plifying carrier frequencies transmitted from east to west. The amplifier is connected through a filter HFW, similar to H Fl-V to the high frequency branch HO of the output connection 0, to the line ML. Low frequency branch L1 is connected through low frequency filter l JFVV to an amplifying tube AWV for amplifying ordinary telephonic frequencies transmitted from east to west. Amplifier A i/V is connected through filter lJl iV, which is similar to LFW to low frequency branch LO of the output connection 0.

ln the operation of the apparatus carrier frequencies incoming from the line ML are transmitted. to the input circuit 1 and pass through the filter HFE to the amplifier A 1 1, being excluded from the amplifier AE by the filter LFE. The amplifier AE amplifies the carrier frequencies which are then transmitted through the filter HFE and over the output connection 0 to the line ML ()rdinary telephonic frequencies incoming from the line ML are transmitted to the input connection .l. and through the filter LFE to the amplifier Al being prevented from reaching the amplifier al by the high frequency filter HFE. After being amplified, the telephonic currents are passed through the filter .lLFE and over the output connection. O to the main line ML Currents incoming from the line Mil are transmitted to the input connection l and separated into the branches LL and H1 by means of the filters trw and HFl/V 'l. he amplifiers AW and A l V then amplify 'the telephonic frequencies and the car-rim frequencies respectively, these frequencies againbeing combine h after passing through the filters LFVV and l-lFW, in the output connection 0 from which they are transmitted to the main line ML l Jhile the invention has been disclosed as applied to a telephone transmission circuit, it is equally applicable to other types of signal transmission, such as, for instance, ordinary telegraph circuits. Where thelow frequency range is quite narrow. the low frequency filters may be replaced by any equivalent means having the desired. selectivity such as tuned circuits or antiresonant combinations. Similarly, if but one carrier channel is superposed on the low frequency transmission line, the high frequency filters HF and HF may be replaced by some simple form of tuning arrangement.

in general, while it has been deemed desir-able in the interest of clear understanding to illustrate the invention as embodied ina specific form of circuit :nrrangement. it will he olwions that the general |u'in ciples; herein disclosed may be employwl in .many other organizations wide y different from those illustrated. without departing from the spirit of the invention as defined in the following claims:

li hat is claimed is l. in a signaling systenn a transmission line, a repeater in said line for amplifying a ban-d of low frequency signaling currents,

a second repeater for said lineoperated in parallel with said first mentioned repeater and adapted to amplify a band of hi frequency oscillations of the order used in carrier current transmission, means associatcd with said first mentioned repeater to substantially prevent the transmission of high frequency currents to said repeater, and means associated with the latter tepeater to substantially prevent the transmission of low frequency signaling currents thereto.

2. In a signaling system, a transmission line, a repeater in said line for amplifying a band of low frequency signaling currents, a second repeater for said line operated in parallel with said first mentioned re eater and adapted to amplify a band of h' frequency oscillations of the order used in carrier current transmission, means associated with said first mentioned repeater to substantially prevent the transmission of frequency currents to said repeater, and a broad band filter associated with the second repeater so arranged as to substantially suppress low frequency signaling currents while freely transmitting to said repeater oscillations of carrier frequency.

3. In a signaling system, a transmission line, a repeater in said line for amplifying a band of low frequency signaling currents,

a second repeater for said line operated in parallel with said first mentioned repeater and adapted to amplify a band of high frequency oscillations of the order used in carrier current transmission, a broad band filter associated with said first mentioned repeater, said filter being so arranged as to substantially suppress carrier frequencies while freely transmitting to said repeater a band of frequencies within the range employed in ordinary signal transmission, and a broad band filter associated with said second repeater, said filter being so arranged as to substantially suppress frequencies below the upper limit of frequencies used in ordinary signal transmission while freely transmitting a band of frequencies above said limit.

4. In a signaling system, a transmission line adapted to transmit currents lyin in different frequency ranges, a plurality 0 repeaters in said line operated in parallel with each other, means in circuit with one repeator for substantially preventing the transmission of frequencies below a preassigned upper limit, and means in circuit with another repeater for substantially preventing the transmission of frequencies above said preassigned limit.

5. In a signaling system, a transmission line adapted to transmit currents lying in different frequency ranges, a plurality of repeaters in said line operated in parallel with each other, a broad band filter in circuit with one repeater, said filter being so arranged as to substantially suppress frequencies below a preassigned upper limit while freely transmitting a band of frequencies above said limit, and a broad band filter in circuit with another repeater, said filter being so arranged as to substantially suppress frequencies above said preassigned upper limit while freely transmitting a band 0 frequencies below said limit.

6. In a signaling sydzem, a transmission line, a repeater in said line for amplifying a band of signaling currents having frequencies lower than the highest frequency used in ordinary telephonic transmission, a second repeater for said line operated in parallel with said first mentioned repeater and adapted to amplify a band of high frequency oscillations (of the order used in carrier current transmission, means associated with said first repeater for substantially preventing the transmission of frequencies above the upper limit of frequencies used in ordinary telephonic transmission, and means associated with said second repeater for substantially preventing the transmission of frequencies below said limit.

7. In a signaling system, a transmission line, a repeater in said line for amplifying a band of signaling currents having frequencies lower than the highest frequency used in ordinary telephonic transmission, a second repeater for said line operated in parallel with said first mentioned re eater and adapted to amplify a band 0 high frequency oscillations of the order used in carrier current transmission, a broad band filter associated with said first mentioned repeater and so arran d as to substantially prevent the transmlssion of frequencies above the upper limit of ordinary telephonic transmission while freely transmitting a band of fre uencies within said limit, and a second broa band filter associated with said second repeater and so arranged as to substantially su press frequencies below said limit while fi'eely transmitting a band of frequencies above said limit.

8. In a transmission system a plurality of repeaters operated in parallel and adapted to amplify different ranges of frequencies, means in the input circuit of each repeater to determine the range of frequencies transmitted to the repeater, a balancing circuit for each re eater, and means in each balancing circui having electrical charac teristics simulating the electrical characteristics of said first mentioned means.

9. In a transmission system a plurality of repeaters operated in parallel and adapted to amplify different ranges of frequencies, means in the input circuit of each repeater to determine the range of fre uencies to be amplified by each repeater, a alancing circuit for each repeater, and means in each balancing circuit having electrical characteristics simulating the electrical characteristics of said first mentioned means.

10. In a transmission system a plurality of repeaters operated in parallel and adapted to amplify different ranges of frequencies, a broad band filter in the input circuit of each repeater a balancing circuit for each repeater, and means in each balancing circuit having electrical characteristics simulating the electrical characteristics of the corresponding filter.

11. In a transmission system a plurality of repeaters operated in parallel and alapted to amplify different ranges of frequencies, a broad band filter in the input circuit of each repeater, a balancing circuit for each repeater, and a broad band filter in each balancing circuit for balancing the corresponding filter in the input circuit.

In testimony whereof, I have signed my name to this specification this 18th day of June 1919.

LLOYD ESPENSCHIED. 

